Pneumatic tire

ABSTRACT

The pneumatic tire described herein is provided with, in a tread surface, at least two circumferential grooves continuously extending in a tread circumferential direction, and a resonator disposed in a land part defined between two circumferential grooves having different sectional areas of the at least two circumferential grooves, the resonator having an air chamber opened to a land part surface in a position separated away from the circumferential groove, one or more narrowed necks communicating the air chamber with one of the two circumferential grooves, and one or more narrowed necks communicating the air chamber with the other circumferential groove, wherein a sectional area S 1  of the narrowed neck of the resonator, opened to a circumferential groove with a relatively large sectional area is larger than a sectional area S 2  of the narrowed neck of the resonator, opened to a circumferential groove with a relatively small sectional area.

TECHNICAL FIELD

This disclosure relates to a pneumatic tire.

BACKGROUND

In recent years, as vehicles have become quiet, vehicle noises caused bythe rolling load of a pneumatic tire have become a large factor ofvehicle noises, and there is a demand for a reduction of such noises.Tire noises of high frequency, particularly of around 1000 Hz havebecome a main cause of vehicle exterior noises, and there has been ademand to reduce such tire noises. This was also desired from theviewpoint of addressing environmental issues.

Tire noises of around 1000 Hz are generated mainly by air columnresonance. Air column resonance sound is a noise generated by resonanceof air in a tube defined by a circumferential groove continuouslyextending in the tread circumferential direction and the road surface.In general vehicles, the sound is generated in the range of around 800Hz to 1200 Hz, and due to the high sound pressure level at the peak andthe wide frequency range, it is a large part of the noises generated bya pneumatic tire. Further, since the human hearing sense is especiallysensitive to noises in a frequency band of around 1000 Hz, a reductionin such air column resonance sound is also effective in terms ofimproving quietness felt by drivers at the time of travelling.

As pneumatic tires with reduced air column resonance sound, for example,a pneumatic tire provided with, in the land part defined bycircumferential grooves, a resonator having an air chamber opened to theland part surface and one narrowed neck communicating the air chamber toa circumferential groove (e.g. PTL 1 (JPH05338411A)), and a pneumatictire provided with, in the land part defined between two circumferentialgrooves, a resonator having an air chamber opened to the land partsurface, one or more narrowed necks communicating the air chamber to oneof the two circumferential grooves, and one or more narrowed neckscommunicating the air chamber to the other circumferential groove (e.g.PTL 2 (JP2007269144A)) have been proposed. It is disclosed that,according to the former pneumatic tire, disposing a resonator wouldenable reducing air column resonance sound generated in acircumferential groove. Further, it is disclosed that, according to thelatter pneumatic tire, since air column resonance sound generated in twocircumferential grooves can be reduced together, the number ofresonators to dispose can be reduced while effectively reducing aircolumn resonance sound compared to the resonator having a narrowed neckopened to one circumferential groove of the former pneumatic tire, andtherefore a decrease in land part rigidity can be prevented.

CITATION LIST Patent Literature

PTL 1: JPH05338411A

PTL 2: JP2007269144A

SUMMARY Technical Problem

With a pneumatic tire provided with, in the land part defined betweentwo circumferential grooves, a resonator having one narrowed neck openedto one of the two circumferential grooves and one narrowed neck openedto the other circumferential groove, for example, when the sectionalareas of each narrowed neck are the same, there were cases where the aircolumn resonance sound is hardly reduced.

It could therefore be helpful to provide a pneumatic tire with improvednoise reduction performance exhibited by a resonator.

Solution to Problem

The pneumatic tire described herein is provided with, in a treadsurface, at least two circumferential grooves, and a resonator disposedin a land part defined between two circumferential grooves havingdifferent sectional areas of the at least two circumferential grooves,the resonator having an air chamber opened to a land part surface in aposition separated away from the circumferential groove, one or morenarrowed necks communicating the air chamber with one of the twocircumferential grooves, and one or more narrowed necks communicatingthe air chamber with the other circumferential groove, wherein asectional area S1 of the narrowed neck (hereinafter referred to as“first narrowed neck”) of the resonator, opened to a circumferentialgroove with a relatively large sectional area is larger than a sectionalarea S2 of the narrowed neck (hereinafter referred to as “secondnarrowed neck”) of the resonator, opened to a circumferential groovewith a relatively small sectional area.

Since the sectional areas of each narrowed neck opened to thecircumferential grooves are different, the resonator is allowed tosufficiently function. Further, since the sectional area of the narrowedneck opened to the side where the sound pressure of air column resonancesound generated in the circumferential groove becomes relatively large,the resonator is allowed to resonate more effectively, and as a result,the noise reduction performance exhibited by the resonator can beimproved.

In the pneumatic tire described herein, sectional area S1 and sectionalarea S2 of the narrowed necks preferably satisfy the relation ofS1/S2≥1.2. By satisfying this relation, it is possible to effectivelyenhance noise reduction performance of the resonator.

For the pneumatic tire described herein, the resonator is not limited toa particular type as long as air column resonance sound is effectivelyreduced. As an example, a Helmholtz-type resonator may be used. In thiscase, the resonator 6 can be modeled as the shape shown in FIG. 2(a),and the resonance frequency f₀ can be expressed by formula (1) whereinthe radius, the length and the sectional area of the narrowed neck 7 areeach expressed as r, l₀, S, the volume of the air chamber 8 is expressedas V, and the speed of sound is expressed as c.

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack & \; \\{f_{0} = {\frac{c}{2\pi}\sqrt{\frac{S}{\left( {1_{0} + {1.3r}} \right)V}}}} & (1)\end{matrix}$

The correction of length of the narrowed neck 7 in the above formula isnormally obtained by experiments, and the value depends on the document.Here, a value of 1.3r is used.

Further, the resonance frequency f₀ in a case of a Helmholz-typeresonator 6 provided with two narrowed necks 7 a and 7 b per one airchamber 8, such as that schematically shown in FIG. 2(b), can similarlybe expressed by formula (2) wherein the radii, the lengths and thesectional areas of the narrowed necks 7 a and 7 b, are each expressed asr_(a) and r_(b), l_(0a) and l_(0b), S_(a) and S_(b), the volume of theair chamber 8 is expressed as V, and the speed of sound is expressed asc.

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack & \; \\{f_{0} = {\frac{c}{2\pi}\sqrt{\frac{\frac{S_{a} + S_{b}}{\left( {\left( {1_{oa} + {1.3r_{a}}} \right) + \left( {1_{ob} + {1.3r_{b}}} \right)} \right)}}{2}V}}} & (2)\end{matrix}$

Therefore, the resonance frequency f₀ of the resonator 6 can be changedas required by selecting the sectional areas S_(a) and S_(b) of thenarrowed necks 7 a and 7 b, the volume V of the air chamber 8, and thelike. Further, as shown in formula (2) with an example of two narrowednecks 7, when there is a plurality of narrowed necks 7, it is known thatthere is no practical problem in calculating by considering itequivalent to one narrowed neck 7 having a total sectional area of theplurality of narrowed necks 7 a and 7 b and an average length of theplurality of narrowed necks 7 a and 7 b.

The sectional areas of the circumferential groove and the narrowed neckare the sectional areas in the cross section along the directionperpendicular to the extending direction of the circumferential grooveand the narrowed neck. In a case where the sectional areas vary, theaverage sectional area (the volumes of the circumferential groove andthe narrowed neck divided by their extending lengths) is used as thesectional area. In a case where there are two or more narrowed necksopened to each circumferential groove for one resonator, the totalsectional area of those narrowed necks is the sectional area S1, S2 ofthe narrowed neck.

Further, unless otherwise specified, the ground contact condition of thetread surface refers to a state where the tire is assembled with anapplicable rim, with a prescribed air pressure applied and a load of 80%of the maximum load applied. The “Applicable rim” is a valid industrialstandard for the region in which the tire is produced or used, andrefers to a standard rim (or “Approved Rim”, “Recommended Rim”) ofapplicable size described in the “JATMA (Japan Automobile TireManufacturers Association) YEAR BOOK” in Japan, “ETRTO (European Tyreand Rim Technical Organisation) STANDARD MANUAL” in Europe, “TRA (THETIRE and RIM ASSOCIATION INC.) YEAR BOOK” in the United States ofAmerica, and the like. A state where “prescribed air pressure is appliedto a tire assembled with an applicable rim” refers to a state where thetire is attached to the above applicable rim, and the air pressureapplied is the air pressure corresponding to the maximum load capacityof a single wheel in applicable size/ply rating (maximum air pressure)described in JATMA and the like. Here, air can be replaced with inertgas such as nitrogen gas, and the like.

Further, unless otherwise specified, various dimensions of the tirerefer to dimensions of the tire assembled with an applicable rim withair pressure applied and no load applied.

Further, “narrowed neck” and “air chamber” used herein both refer tothose which open in the ground contact surface under the previouslymentioned ground contact conditions.

Advantageous Effect

It is possible to provide a pneumatic tire with improved noise reductionperformance exhibited by a resonator.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a partially developed plan view of a tread pattern of thepneumatic tire according to one embodiment;

FIG. 2A schematically shows a Helmholtz-type resonator with one narrowedneck, and FIG. 2B schematically shows a Helmholtz-type resonator withtwo narrowed necks;

FIG. 3A and FIG. 3B are perspective views illustrating embodiments offorming the resonator in the pneumatic tire of FIG. 1;

FIG. 4A to FIG. 4C are e developed plan views similar to FIG. 1 ofmodified examples of each of the narrowed neck and the air chamber inthe pneumatic tire of FIG. 1;

FIG. 5 is a developed plan view similar to FIG. 1 of a modified exampleof the extending direction from the air chamber of the narrowed neck inthe pneumatic tire of FIG. 1.

DETAILED DESCRIPTION

The following describes one embodiment of the disclosure in detail withreference to the drawings.

FIG. 1 is a partially developed plan view of a tread pattern ofpneumatic tire 1 according to one embodiment of the disclosure. Sincethe internal reinforcing structure and the like of the tire are similarto those of a general radial tire, they are not illustrated.

In a pneumatic tire 1 according to one embodiment of the disclosure, atleast two circumferential grooves 3 continuously extending substantiallyin the tread circumferential direction are provided on a tread surface2. In FIG. 1, four circumferential grooves 3 are provided on a treadsurface 2. FIG. 1 shows a form where the circumferential grooves 3extend in a linear manner along the tread circumferential direction.However, as long as the circumferential grooves 3 extend continuously inthe tread circumferential direction, any form of extending for example,a zigzag form, wave-like form or the like may be adopted.

Further, on the tread surface 2, as shown in FIG. 1, three rows ofrib-shaped land parts 4 are defined in the inner side in the tire widthdirection by circumferential grooves 3 adjacent to each other, and tworows of rib-shaped land parts 4 are defined in the outer side in thetire width direction (shoulder parts) by the circumferential groove 3and the ground contact end in the outer side in the tire width directionof the tread surface 2. Further, two of the three rows of rib-shapedland parts 4 in the inner side in the tire width direction are definedby two circumferential grooves 3 a and 3 b which have differentsectional areas. In the circumferential grooves 3 disposed on the treadsurface 2 shown in FIG. 1, from the viewpoint of ensuring drainageperformance of the pneumatic tire 1, the sectional area of thecircumferential groove 3 a located in the inner side in the tire widthdirection is larger than the sectional area of the circumferentialgroove 3 b in the outer side in the tire width direction. However, it isalso possible to make the sectional area of the circumferential groove 3b in the outer side in the tire width direction larger than thesectional area of the circumferential groove 3 a located in the innerside in the tire width direction. Further, as shown in FIG. 1, thelarge/small relation between the respective sectional areas of the twocircumferential grooves 3 a and 3 b is created by varying the groovewidth of the circumferential grooves. However, the relation can becreated by varying the depth, or both the width and the depth of eachcircumferential groove.

In the rib-shaped land part 4 a defined between two circumferentialgrooves 3 a and 3 b having different sectional areas, as shown in FIG.1, a resonator 5 having an air chamber 5 a opened to the land partsurface in a position separated away from the circumferential groove 3,a narrowed neck 5 b communicating the air chamber 5 a with one of thetwo circumferential grooves 3 a and 3 b, and a narrowed neck 5 bcommunicating the air chamber 5 a with the other circumferential groove,is disposed. Further, as shown in FIG. 1, one narrowed neck 5 b isopened to one circumferential groove 3 and the other circumferentialgroove 3 respectively. However, it is also possible to make two or morenarrowed necks 5 b opened to one circumferential groove 3 and the othercircumferential groove 3, respectively or only in one side.

Meanwhile, with a resonator comprising one or more narrowed necks openedto one circumferential groove, and one or more narrowed necks having thesame sectional area as said narrowed neck(s), opened to the othercircumferential groove, there were cases where the air column resonancesound was hardly reduced.

Therefore, in the pneumatic tire 1 of the disclosure, the resonator 5 isformed so that the sectional area S1 of the narrowed neck (firstnarrowed neck) 5 c which opens to the circumferential groove 3 a with arelatively large sectional area is larger than the sectional area S2 ofthe narrowed neck (second narrow neck) 5 d which opens to thecircumferential groove 3 b with a relatively small sectional area.

With this pneumatic tire 1, among the dimensions and shapes of thenarrowed neck 5 b and air chamber 5 a constituting the resonator 5,particularly, the sectional areas S1 and S2 of each narrowed neck 5 bopened to the circumferential grooves 3 are varied. Therefore, resonancefrom the resonator 5 generated respectively via the narrowed neck 5 c ofthe resonator 5, opened to the circumferential groove 3 a with arelatively large sectional area and the narrowed neck 5 d of theresonator 5, opened to the circumferential groove 3 b with a relativelysmall sectional area would not cancel each other, and accordingly theresonator 5 is allowed to sufficiently function. Further, since thesectional area of the narrowed neck 5 b opened to the side where thesound pressure of air column resonance sound generated in thecircumferential groove 3 becomes relatively large i.e. thecircumferential groove 3 a with a relatively large sectional area, theresonator 5 is allowed to resonate more effectively, and therefore thenoise reduction performance exhibited by the resonator 5 can beimproved. Further, by improving the noise reduction performance of theresonator 5, for example, the number of resonators 5 to dispose in thetread surface 2 can be reduced to improve rigidity in land parts 4 whilemaintaining an equivalent noise reduction performance, and therefore thesteering stability of the tire 1 can be enhanced. Further, flexibilityin the terms of designs of the tread pattern can be enhanced. Forexample, various types of resonators 5 having different resonancefrequency can be disposed in the tread surface 2.

In the pneumatic tire 1 described herein, as long as the sectional areasof the two circumferential grooves 3 a and 3 b defining the rib-shapedland part 4 a with the resonator 5 disposed thereon are different fromeach other, the sectional areas of circumferential grooves 3 other thanthe two circumferential grooves 3 a and 3 b having different sectionalareas may be made the same as each other or different from each other.Further, in tread surface 2, other resonators comprising an air chamberand a narrowed neck may be disposed in the rib-shaped 1 and parts 4 inthe center side in the tire width direction and the outer side in thetire width direction shown in FIG. 1.

Further, as shown in FIG. 1, the large/small relation between respectivesectional areas S1, S2 of the first narrowed neck 5 c and the secondnarrowed neck 5 d is created by varying the width of each narrowed neck.However, the relation can be created by varying the depth, or both thewidth and the depth of each narrowed neck.

Here, the sectional area S1 of the first narrowed neck 5 c and thesectional area S2 of the second narrowed neck 5 d preferably satisfy therelation of S1/S2≥1.2. By satisfying this relation, the phenomenon wherethe resonance from the resonator 5 generated through the first andsecond narrowed necks 5 c and 5 d cancel each other is more effectivelysuppressed, and the resonator 5 is allowed to further sufficientlyfunction. Further, it is possible to allow the resonator 5 to moreeffectively function against the air column resonance sound with arelatively large sound pressure, generated in the circumferential groove3 a having a relatively large sectional area.

Although the upper limit of the ratio of the sectional area S1 of thefirst narrowed neck 5 c to the sectional area S2 of the second narrowedneck 5 d is not limited, if the sectional area S1 of the first narrowedneck 5 c is excessively larger than the sectional area S2 of the secondnarrowed neck 5 d, it tends to be difficult to form the resonator 5 sothat it has a desired resonance frequency. Therefore, it is morepreferable that the sectional area S1 of the first narrowed neck 5 c andthe sectional area S2 of the second narrowed neck 5 d satisfy therelation of 3≥S1/S2≥1.2. Further, as mentioned above, from the viewpointof easily forming the resonator 5 so that it has a desired resonancefrequency while allowing the resonator 5 to more effectively function,it is further preferable that the sectional area S1 of the firstnarrowed neck 5 c and the sectional area S2 of the second narrowed neck5 d satisfy the relation of 2≥S1/S2≥1.2.

Regarding the narrowed neck 5 b and the air chamber 5 a of the resonator5, as long as they open to the road surface in the ground contactsurface under the ground contact conditions mentioned above, and adesired resonance frequency is generated, the width, depth, form ofextending, or the like are not particularly limited. Regarding thenarrowed neck 5 b, for a tire assembled with an applicable rim and in astate where prescribed air pressure is applied and no load is applied,for example, the width opened to the land part surface is preferably inthe range of 0.5 mm to 2.0 mm, and more preferably in the range of 0.7mm to 2.0 mm. From the viewpoint of forming the resonator 5 so that ithas a desired resonance frequency and allowing it to sufficientlyfunction, the depth from the tread surface 2 of the narrowed neck ispreferably ⅓ to ½ of the depth from the tread surface 2 of thecircumferential groove 3 to which the narrowed neck 5 b opens. The crosssectional shape along the direction perpendicular to the extendingdirection of the narrowed neck 5 b, as shown in FIG. 3, can be formed asfor example, squares such as rectangles (FIG. 3(a)), or a so-calledflask shape having an enlarged part in the bottom part of the narrowedneck 5 b (FIG. 3(b)). The form of extending of the narrowed neck 5 b, asshown in FIG. 4(a), can be a straight shape, a bent shape, a curvedshape or a combination thereof. Although not shown in the drawings, thesidewalls of the narrowed neck 5 b may be provided with a plurality ofprojections projected from the sidewalls, to prevent the narrowed neck 5b from unexpectedly closing.

Regarding the dimension, shape and the like of the above narrowed neck 5b, each of the plurality of narrowed necks 5 b of one resonator 5 may bemade so that they are the same as each other or different from eachother. Further, the dimension, shape and the like of the narrowed necks5 b of a plurality of resonators 5 in one row of rib-shaped 1 and parts4 a or in different rib-shaped land parts 4 a, may be made so that theyare the same as each other or different from each other.

Further, regarding the air chamber 5 a of the resonator 5, as shown inFIG. 4(a), the opening shape of the air chamber 5 a to the surface ofthe land part 4 a can be made a shape of a polygonal outline, or a shapeof a curved outline such as a round shape, oval shape and the like.Further, the shape of the bottom part of the air chamber 5 a can be madea flat shape, a curved shape and the like. Further, the opening shapesand the like of the each air chamber 5 a of the plurality of resonators5 in one row of rib-shaped land parts 4 a or in different rib-shapedland parts 4 a can be made the same as or different from each other.

In FIG. 4(b), the dimensions of the air chambers 5 a are varied to varythe resonance frequencies of the resonators 5. However, as mentionedabove, by varying the dimensions, shapes and the like of the narrowednecks 5 b and/or the air chambers 5 a of the resonators 5, a pluralityof resonators 5 each having different resonance frequencies can bedisposed in the rib-shaped land parts 4 a of the tread surface 2.

To form a resonator 5 disposed in the tread surface 2 so that it has adesired resonance frequency and to allow it to sufficiently function,and for example, to open every narrowed neck 5 b of the resonator 5 tothe road surface in the ground contact surface under the ground contactconditions mentioned above, the total number of first narrowed necks 5 cand second narrowed necks 5 d of a resonator 5 is preferably two tofour.

The resonator 5 shown in FIG. 4(c) has two first narrowed necks 5 c andone second narrowed neck 5 d, and more first narrowed necks 5 c aredisposed compared to second narrowed necks 5 d. However, it is alsopossible to dispose more second narrowed necks 5 d than first narrowednecks 5 c.

For the pneumatic tire 1 described herein, the extending direction ofeach of the first narrowed neck 5 c and the second narrowed neck 5 d tothe air chamber 5 a is not particularly limited. However, from theviewpoint of reducing the pitch noise generated when the edges opened tothe land part surface, of the narrowed neck 5 b and the air chamber 5 acollides with the road surface when the tire 1 rolls, it is preferablethat each of the first narrowed neck 5 c and the second narrowed neck 5d do not extend toward the inner side in tread circumferential directionwith respect to the air chamber 5 a as shown in FIG. 5, but that theyextend toward the outer side in tread circumferential direction withrespect to the air chamber 5 a as shown in FIG. 1. In other words, it ispreferable to extend narrowed necks 5 c, 5 d with reduced overlapping ofnarrowed necks 5 c, 5 d and air chamber 5 a in the width direction ofthe rib-shaped land parts 4 a. Further, from such viewpoint, as shown inFIG. 1, narrowed necks 5 c, 5 d are preferably extended from the outerend position in tread circumferential direction of the air chamber 5 ato the outer side in tread circumferential direction and opened tocircumferential grooves 3 a, 3 b.

In FIG. 1, regarding resonators 5 disposed in the tread surface 2,resonators 5 in one rib-shaped land part 4 a are positioned so as to bedeviated to resonators in the other rib-shaped land part 4 a, in thetread circumferential direction. However, they may be disposed in thesame position in the tread circumferential direction.

In the rib-shaped land parts 4 a defined between two circumferentialgrooves 3 a and 3 b having different sectional areas, it is possible todispose, in addition to a resonator 5 having a first narrowed neck 5 cand a second narrowed neck 5 d, a resonator with only one narrowed neckand/or a resonator wherein the respective sectional areas of the firstnarrowed neck and the second narrowed neck are the same.

Embodiments of the disclosure have been explained with reference to thedrawings. However, the pneumatic tire disclosed herein is not intendedto be limited to the above examples and may be modified as appropriate.

Examples

Although the disclosure will be described below in further detail withreference to examples, the disclosure is not intended to be limited inany way to the following examples.

Sample tires of examples according to an embodiment of the disclosureand sample tires of comparative example were prepared, and the followingexperiments 1 to 3 were conducted.

[Experiment 1]

In experiment 1, using pneumatic tires provided, in the tread surface,with four circumferential grooves extending in the tread circumferentialdirection with the sectional area of the two circumferential grooves inthe inner side in tire width direction being larger than that of the twocircumferential grooves in the outer side in the tire width direction,and having a Helmholtz-type resonator in the rib-shaped land partdefined between two circumferential grooves having different sectionalareas, the following sample tires with the respective sectional areas ofone first narrowed neck and one second narrowed neck of the resonatorvaried were prepared. With these tires, the reduction effect of aircolumn resonance sound generated in the circumferential groove wasconfirmed by a noise test.

The tire of example 1 is a pneumatic tire for an automobile with a tiresize of 195/45R15 having a tread pattern shown in FIG. 1, wherein twocircumferential grooves in the inner side in the tire width directionhave a sectional area of 80 mm² (width 10 mm, depth 8 mm), twocircumferential grooves in the outer side in the tire width directionhave a sectional area of 64 mm² (width 8 mm, depth 8 mm). Further,regarding the resonator, the sectional area of the first narrowed neckis 3.3 mm² (width 0.83 mm, depth 4 mm), the length of the first narrowedneck is 10 mm, the sectional area of the second narrowed neck is 3 mm²(width 0.75 mm, depth 4 mm), the length of the second narrowed neck is10 mm, the volume of the air chamber is 1560 mm³, the resonancefrequency thereof is 1020 Hz, and fifty-two of them were disposed in onerow of rib-shaped land parts.

Other than that the sectional areas of the first narrowed neck and thesecond narrowed neck were changed to specifications shown in Table 1 andthat each dimension of the narrowed neck was adjusted so that theresonance frequency is the same as that of the tire of example 1, thetires of examples 2 to 6 were prepared in the same way as the tires ofexample 1.

Further, other than that the sectional areas of the first narrowed neckand the second narrowed neck were changed to specifications shown inTable 1 and that each dimension of the narrowed neck was adjusted, thetires of comparative examples 1 and 2 were prepared in the same way asexample 1.

When performing the noise test for air column resonance sound, the abovetires were attached to a rim with a size of 7.5 J-15, applied with airpressure of 180 kPa inside, and then mounted onto a vehicle. The vehiclewas driven at a constant speed of 80 km/h, and then the engine wasstopped to allow the vehicle to coast. At a position 7.5 m sideward fromthe center of the vehicle and a height from the ground of 1.2 m, lateralnoise was measured in accordance with conditions specified by JASO C606,and overall values of the center frequency band of 800 Hz-1000 Hz-1250Hz in the ⅓ octave band were obtained. Smaller overall values indicatelarger noise reducing effect of the resonator disposed in the treadsurface of the pneumatic tire. The results are shown in Table 1.

The resonators disposed on these sample tires satisfy the above formulas(1) and (2), and the speed of sound c was 343.7 m/s.

TABLE 1 Sectional Area S1 Sectional Area S2 Volume of Sectional Area ofNoise of First of Second Air Resonance Circumferential Test S1/ NarrowedNeck Narrowed Neck Chamber Frequency Groove (dB) S2 (mm) (mm ) (mm³)(Hz) (mm²) Compar- 65.2 0.9 2.7 3 1560 1000 80/64 ative Example 1Compar- 65.5 1 3 3 1560 1010 80/64 ative Example 2 Example 1 65 1.1 3.33 1560 1020 80/64 Example 2 64.5 1.2 3.6 3 1560 1000 80/64 Example 364.6 1.4 4.2 3 1560 990 80/64 Example 4 64.7 2.9 4.35 1.5 1560 100080/64 Example 5 64.7 3 4.5 1.5 1560 1010 80/64 Example 6 64.9 3.1 4.651.5 1560 1020 80/64

As a result of this test, it was revealed that, for the tires ofexamples 1 to 6, since the sectional area of the first narrowed neck wasmade larger than the sectional area of the second narrowed neck, aircolumn resonance sound is reduced compared to the tire of comparativeexamples 1 and 2. Further, it was revealed that, for the tires ofexamples 2 to 6, the sectional area S1 of the first narrowed neck andthe sectional area S2 of the second narrowed neck were set to satisfy arelation of S1/S2≥1.2, and therefore air column resonance sound isfurther reduced compared to the tire of example 1.

[Experiment 2]

In experiment 2, using the tire of example 2, and without changing theresonance frequency of the resonators and the relation between the totalsectional area of the first narrowed necks and the total sectional areaof the second narrowed necks, the numbers of the first narrowed necksand the second narrowed necks were changed to prepare the followingsample tires, and the reduction effect of air column resonance soundgenerated in the circumferential groove was confirmed by a noise test.

Other than the changes described below, the following tires wereprepared in the same way as the tire of example 2. Regarding the tire ofexample 7, the number of first narrowed necks was changed to two.Regarding the tire of example 8, the number of second narrowed necks waschanged to two. Regarding the tire of example 9, the numbers of firstnarrowed necks and second narrowed necks were each changed to two.

Further, the noise test was performed in the same way as the abovedescribed method. The results are shown in Table 2.

TABLE 2 First Narrowed Neck Second Narrowed Neck Number Number Noise ofSectional of Sectional Test S1/ Narrowed Area S1′ Narrowed Area S2′ (dB)S2 Necks (mm²) Necks (mm²) Compar- 65.5 1 1 3 1 3 ative Example 2Example 2 64.5 1.2 1 3.6 1 3 Example 7 64.5 1.2 2 1.8 1 3 Example 8 64.51.2 1 3.6 2 1.5 Example 9 64.5 1.2 2 1.8 2 1.5 *Sectional areas S1′ andS2′ indicate the respective sectional areas of one narrowed neck. Here,S1 = S1′ × number of narrowed necks, S2 = S2′ × number of narrowednecks.

As a result of this test, it was revealed that, with the tires ofexamples 2, and 7 to 9, even if the number of narrowed necks is changed,the air column resonance sound is reduced compared to the tire ofcomparative example 2.

[Experiment 3]

In experiment 3, using the tire of example 2, the respective extendingdirections from the air chamber of the first narrowed neck and thesecond narrowed neck were directed toward the inner side in the treadcircumferential direction with respect to the air chamber to prepare asample tire of example 10 having a tread pattern shown in FIG. 5, andthe reduction effect of air column resonance sound generated in thecircumferential groove and pitch noise was confirmed by a noise test.

In the noise test for pitch noise, measurement was conducted in the sameway as the noise test for air column resonance, and as the pitch noisefrequency varies depending on the speed of the vehicle, circumferentiallength of the tire, number of resonators, and the like, the overallvalues of a center frequency value of 630 Hz, in the ⅓ octave band weredetermined as the pitch noise and the values thereof were obtained foreach sample tire. The smaller overall values indicate that more pitchnoise is reduced. The results are shown in Table 3.

TABLE 3 Extending Noise Direction from Air Test Chamber of (dB) S1/S2Narrowed Neck Example 2 64.5 1.2 Outer Side in Circumferential DirectionExample 10 65.6 1.2 Inner Side in Circumferential Direction

As a result of this test, with the tire of example 2, since therespective extending directions from the air chamber of the firstnarrowed neck and the second narrowed neck were directed toward theouter side in the tread circumferential direction with respect to theair chamber, the pitch noise is reduced compared to the tire of example10.

INDUSTRIAL APPLICABILITY

It is possible to provide a pneumatic tire with improved noise reductionperformance exhibited by a resonator.

REFERENCE SIGNS LIST

1 Pneumatic tire

2 Tread surface

3 Circumferential groove

3 a Circumferential groove (with relatively large sectional area)

3 b Circumferential groove (with relatively small sectional area)

4 Rib-shaped land part

4 a Rib-shaped land part (defined between two circumferential grooveshaving different sectional areas)

5 Resonator

5 a Air chamber

5 b Narrowed neck

5 c Narrowed neck (opened to circumferential groove with relativelylarge sectional area)

5 d Narrowed neck (opened to circumferential groove with relativelysmall sectional area)

6 (Modeled) resonator

7, 7 a, 7 b Narrowed neck (of modeled resonator)

8 Air chamber (of modeled resonator)

S1 Sectional area of narrowed neck (opened to circumferential groovewith relatively large sectional area)

S2 Sectional area of narrowed neck (opened to circumferential groovewith relatively small sectional area)

The invention claimed is:
 1. A pneumatic tire provided, in a treadsurface, with at least two circumferential grooves continuouslyextending in a tread circumferential direction, and a resonator disposedin a land part defined between first and second circumferential grooveshaving different sectional areas, the resonator having an air chamberopened to a land part surface in a position separated away from thefirst and second circumferential grooves, one or more narrowed neckscommunicating the air chamber with one of the first and secondcircumferential grooves, and one or more narrowed necks communicatingthe air chamber with the other of the first and second circumferentialgrooves, wherein the first circumferential groove has a larger sectionalarea than that of the second circumferential groove, a sectional area S1of the narrowed neck of the resonator, opened to the firstcircumferential groove is larger than a sectional area S2 of thenarrowed neck of the resonator, opened to the second circumferentialgroove, and wherein the sectional area S1 and the sectional area S2 ofthe narrowed necks satisfy a relation of 3≤S1/S2≤1.2, the firstcircumferential groove is located in an inner side in a tire widthdirection with respect to the second circumferential groove, and thenumber of the narrowed necks opened to the first circumferential grooveis larger than the number of the narrowed necks opened to the secondcircumferential groove.